Hybrid vehicle power control apparatus and hybrid construction equipment using the power control apparatus

ABSTRACT

An object of the invention is to maintain high vehicle driving performance and system efficiency by preventing reductions in the traction characteristic and the maximum driving speed of a vehicle. 
     The invention relates to an electrical system for an electric automotive vehicle for driving the vehicle by supplying an electric power of a direct-current power supply to an electric motor for driving wheels via a semiconductor power converter for driving the wheels such as an inverter and speed-variably driving this electric motor or an electrical system for an electric automotive vehicle using an engine and a direct-current power supply as driving sources. A booster chopper  200  is connected between a battery device  1  or  4  as the direct-current power supply and an inverter  2  or a semiconductor power converter  100 , and is controlled so that a direct-current input voltage of the inverter  2  or the like becomes substantially constant.

TECHNICAL FIELD

This invention relates to a power control apparatus for use in a hybridvehicle loaded with an engine and an electric motor, and a hybridconstruction machine loaded with such a power control apparatus.

BACKGROUND ART

Heretofore, there have been proposed a variety of hybrid vehicles eachof which is mounted with an engine and an electric motor and which is soconstructed as to drive a load by the motor, and some of these hybridvehicles are in practical use.

For instance, there is proposed a hybrid vehicle in which a battery ischarged with electric power generated from a generator by driving of anengine, and the electric motor is selectively driven either by electricpower from the battery or electric power from the generator.

In the above-constructed hybrid vehicle, it is desirable to optimallycontrol power distribution between the battery and the generatordepending on electric power demanded from a load by way of the motor,considering various requirements such as securing stable operation ofthe engine, attaining output efficiency of the generator, and improvingefficiency of the battery, and preventing deterioration of performanceof the battery by suppressing generation of excessivecharging/discharging currents.

As an apparatus for attaining the aforementioned power control, JapaneseUnexamined Patent Publication No. 5-146008 proposes an arrangement inwhich an output terminal of a generator and an output terminal of abattery are respectively directly connected with a direct-current (DC)line, and output power from the generator is varied by controlling afield current of the generator in such a manner that the output voltageof the generator is set at a target value. With this arrangement, powerdistribution between the battery and the generator is controllablyregulated.

Further, proposed is a hybrid construction machine loaded with an engineand an electric motor to drive an actuator by the motor. For instance,Japanese Unexamined Patent Publication No. 2000-283107 proposes a hybridhydraulic excavator constructed such that power required for drivingplural actuators is selectively supplied by way of the electric motorfrom a generator and a battery.

Generally, in a construction machine, particularly, in a hydraulicexcavator for performing excavation by use of a working attachment, aload-driving torque which is to be outputted from an electric motor inorder to drive an actuator (hydraulic cylinder) of the attachment isgreatly varied depending on various factors such as a reactive forceexerted from an object for excavation and the posture of the attachment,which resultantly increases a difference between a minimal load and amaximal load. Further, since the operating speed of each attachment isfrequently adjusted by an operator, power required for driving a load ischanged on time-basis. FIG. 8 illustrates an example of change of powerdemanded from a load with time at the time of excavating and charging bya hydraulic excavator. As is obvious from FIG. 8, power demand from aload is frequently and greatly changed between the minimal value and themaximal value.

In view of the above, even if the arrangement of the aforementionedJapanese Publication No. 5-146008 is applied to a hybrid vehicle inwhich power demand from a load is greatly changed, e.g. hybridconstruction machine, the following matters should be considered becausethe above publication has the arrangement that the output terminal ofthe generator and the output terminal of the battery (storage device)are respectively directly connected with a DC line:

i) output distribution between the generator and the battery isdetermined based on a relation between a terminal voltage of thegenerator (battery), and an output impedance during a rise-up perioduntil control keeps up with the change of the power demand; and

ii) the voltage and the current of the DC line greatly fluctuatedepending on accumulated electric energy and the level ofcharging/discharging currents of the battery.

Due to the reason i), it is highly likely that the hybrid constructionmachine adopting the arrangement of the aforementioned publication mayencounter an uncontrollable state if the power demand from the load isdrastically changed. As a result, excessive power may be supplied fromthe generator, which may increase burden on the engine for driving thegenerator. Then, it is highly likely that fuel consumption rate or fuelefficiency of the engine may be lowered, or in a worst case, driving ofthe engine may be forcibly suspended owing to overload of the engine.Further, power loss due to internal resistance of the battery may beincreased, or performance of the battery may be deteriorated owing toincrease of charging/discharging currents of the battery.

Generally, means for driving a motor is electrically connected with a DCline. Considering a withstand voltage or a withstand current of acircuit element (e.g. semiconductor switches and diodes such as MOS-FETsor IGBTs) used in such motor-driver, it is required to adopt an elementwhose rated voltage is higher than the maximal value of the voltage ofthe DC line and whose rated current is regulated in accordance with theoutput current of the motor-driver.

Due to the reason ii), as the maximal voltage of the DC line increases,a circuit element having a high withstand voltage is required. As aresult, the cost of the circuit element is raised, and the motor-driverbecomes expensive. Further, if demanded power from the load is to besupplied in the above arrangement by way of the motor in an attempt tocope with a condition that the voltage of the DC line is lowered, theoutput current of the motor-driver is increased. In view of this, acircuit element having a large current capacity is required. Therefore,as with the former case, the cost for the circuit element is raised,which makes the motor-driver expensive. Furthermore, as the outputcurrent of the motor-driver increases, switching loss of a semiconductorswitching element increases, which resultantly increases calorificpower. Accordingly, the size of the motor-driver becomes large owing toincrease of the size of cooling means such as a heat sink which ismounted on the semiconductor switching element. As a result, themotor-driver in its entirety becomes large, and a large space isrequired to load such a large motordriver in a hybrid vehicle.

In view of the above, it is an object of the invention to solve theaforementioned problems residing in the prior art and to provide a powercontrol apparatus for use in a hybrid vehicle that enables to allow agenerator and storage device to optimally supply power just enough fordemanded power from a load even in the case where the demanded powerfrom the load by way of an electric motor is drastically changed, and ahybrid construction machine loaded with such a power control apparatus.

It is another object of the invention to provide a power controlapparatus for use in a hybrid vehicle that enables to improvecharging/discharging efficiency of storage device, to preventdeterioration of performance of the storage device, and to downsize thepower control apparatus, and a hybrid construction machine loaded withsuch a power control apparatus.

DISCLOSURE OF THE INVENTION

One aspect of the invention is directed to a power control apparatus foruse in a hybrid vehicle provided with an engine, a generator driven bythe engine, at least one storage device, an electric motor which isdriven by power supplied from at least one of the generator and thestorage device, and a load which is operated by the motor as a drivesource. The power control apparatus comprises: first power converterwhich is provided between the generator and a direct-current (DC) linefor converting the power outputted from the generator to DC power tooutput the DC power to the DC line; at least one second power converterwhich is provided between the storage device and the DC line forconverting the power outputted from the storage device to DC power tooutput the DC power to the DC line; motor driver which is electricallyconnected with the DC line for driving the motor based on the powersupplied by way of the DC line; and power controller for controlling thefirst power converter and the second power converter to output DC powercorresponding to demanded power from the load by way of the motor to theDC line, wherein the power controller controls the first power converterand the second power converter to maintain a voltage of the DC line at asubstantially constant level irrespective of variation of the powerdemand from the load.

In the above arrangement, the first power converter is provided betweenthe generator and the DC line, and the second power converter isprovided between the storage device and the DC line, and the first powerconverter and the second power converter are controlled to output the DCpower corresponding to the demanded power from the motor-driver to theDC line. With this arrangement, even if power demand from the load byway of the motor is abruptly changed, power just enough for the demandedpower is supplied from the generator or from the storage device. Sincethe voltage of the DC line is maintained at a substantially constantlevel, there is no need of considering level variation of current orvoltage. Thereby, this arrangement facilitates setting of the voltagerating and current rating of circuit elements used in the first powerconverter, the second power converter, and the motor-driver, and makesit possible to produce the circuit element, and the first and secondpower converter and the motor-driver incorporated with such a circuitelement with a reduced size and at a low cost.

Another aspect of the invention has a feature that the power controllercontrols the first power converter to output the DC power of a value notlarger than a predetermined value. This arrangement can obviatedrawbacks such as lowering of fuel efficiency due to increase of aburden to the engine for driving the generator beyond a predeterminedlevel, and forcible suspension of driving of the engine due to overloadof the engine.

Another aspect of the invention has a feature that the power controllercontrols the storage device to discharge an electric current of a valuenot larger than a predetermined value and to charge an electric currentof a value not larger than predetermined values. This arrangement canobviate drawbacks such as lowering of charging/discharging efficiencydue to increase of the charging/discharging currents of the storagedevice beyond the predetermined values, respectively, deterioration ofperformance of the storage device, and shortening of the useful life ofthe storage device.

Another aspect of the invention has a feature that the power controllercontrols the second power converter to output the DC power in such amanner that the storage device outputs a DC voltage of a value notlarger than a predetermined value. In this arrangement, obviated aredrawbacks such as deterioration of performance of the storage device andbreakage thereof by setting the DC voltage at a value not larger than awithstand voltage of the storage device. This arrangement makes itpossible to adopt a component such as an electric double layer capacitorin which a terminal voltage is greatly varied depending on accumulatedelectric energy of the storage device, as the storage device.

Another aspect of the invention has a feature that the power controllercontrols the second power converter to output the DC power in such amanner that said storage device outputs a DC voltage of a value notsmaller than a predetermined value. According to this arrangement, sincethere is no likelihood that the terminal voltage of the storage deviceis not larger than the predetermined value, this arrangement can obviatea phenomenon that the terminal voltage is greatly lowered with theresult that charging/discharging efficiency of the storage device islowered due to increase of input/output current at the time ofinputting/outputting constant power. This arrangement makes it possibleto adopt a component such as an electric double layer capacitor in whicha terminal voltage is greatly varied depending on accumulated electricenergy of the storage device, as the storage device.

Another aspect of the invention has a feature that the power controllercontrols the second power converter to output the DC power in such amanner that electric energy stored in the storage device lies in apredetermined range. This arrangement can obviate drawbacks such asdeterioration of performance of the storage device due to excessivecharging or excessive discharging, and breakage of the storage device.

Another aspect of the invention has a feature that: the power controllerincludes a first controller for sending an electrical command signal tothe first power converter, and a second controller for sending anelectrical command signal to the second power convener; the first powerconverter outputs the DC power responsive to the electrical commandsignal from the first controller; the second power converter outputs theDC power responsive to the electrical command signal from the secondcontroller; and the first controller and the second controllerrespectively send the electrical command signals that are operative tomaintain the voltage of the DC line at a substantially constant level.

In the above arrangement, the first controller is allowed to send anelectrical command signal, e.g., a current command value, which enablesto maintain the voltage of the DC line at a substantially constantlevel, to the first power converter, which in turn outputs the DC powercorresponding to the inputted electrical command signal, and the secondcontroller is allowed to send an electrical command signal, e.g., acurrent command value, which enables to maintain the voltage of the DCline at a substantially constant level, to the second power converter,which in turn outputs the DC power corresponding to the inputtedelectrical command signal. This arrangement secures power supply fromthe generator or from the storage device just enough for the demandedpower from the motor.

Another aspect of the invention has a feature that the power controlapparatus further comprises a plurality of storage device, and aplurality of second power converter corresponding to the plurality ofstorage device in number. In this arrangement, since the plurality ofsecond power convener are provided between the respective correspondingstorage device and the DC line, power supplying and receiving among theplurality of storage device does not occur. This arrangement can obviatelowering of control efficiency of the power control apparatus as a wholedue to energy loss resulting from such power supplying and receiving.

Another aspect of the invention has a feature that, in the arrangementof claim 8, the power controller controls the plurality of second powerconverter in accordance with a predetermined order of priority based oninput/output characteristics of each of the plurality of storage device.This arrangement provides optimal power distribution depending on theinput/output characteristics of each storage device.

Another aspect of the invention has a feature that the load of the powercontrol apparatus includes an actuator for actuating a workingattachment mounted on a main body of the hybrid vehicle. In thisarrangement, even if power demand from the actuator by way of the motoris frequently and greatly varied, power just enough for the demandedpower is suppliable from the generator or from the storage device.

Another aspect of the invention has a feature that a hybrid constructionmachine is incorporated with the power control apparatus for use in thehybrid vehicle as set forth in any one of claims 1 to 9 and that theload of the hybrid construction machine includes an actuator foractuating a working attachment mounted on a main body of the hybridconstruction machine.

In the above arrangement, provided is a hybrid construction machinewhich enables to carry out power supply just enough for the demandedpower from the generator or from the storage device even if the powerdemand from the actuator by way of the motor is frequently and greatlyvaried.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit block diagram showing an electrical configuration ofa first embodiment of a power control apparatus for use in a hybridvehicle in accordance with the invention;

FIG. 2 is a circuit block diagram showing an electrical configuration ofa chopper circuit in FIG. 1;

FIG. 3 is a flowchart showing a first half of a control procedure of aCPU of a power control circuit in the first embodiment of the invention;

FIG. 4 is a flowchart showing a second half of the control procedure ofthe CPU of the power control circuit in the first embodiment of theinvention;

FIG. 5 is a flowchart showing a first half of a control procedure of aCPU of a power control circuit in a second embodiment of the invention;

FIG. 6 is a flowchart showing a second half of the control procedure ofthe CPU of the power control circuit in a second embodiment of theinvention;

FIG. 7 is a diagram showing the entirety of a hybrid hydraulic excavatoras an embodiment of a hybrid construction machine in accordance with theinvention; and

FIG. 8 is a graph showing an example of change of power demand from aload with time at the time of excavating and charging by a hydraulicexcavator.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the invention are described withreference to FIGS. 1 through 7.

(a) First Embodiment

A power control apparatus in accordance with the first embodiment of theinvention is comprised of, as shown in FIG. 1, an engine 1, analternate-current (AC) generator 2, an electric motor 10, a load 11, andan electric circuit section 100.

The engine 1 is directly connected with the AC generator 2. The ACgenerator 2 outputs three-phase AC power by being driven by the engine1.

The motor 10 may be an induction motor, a direct-current (DC) motor, asynchronous motor, or its equivalent.

The load 11 includes a hydraulic pump 12 and an actuator 13. Thehydraulic pump 12 is drivingly rotated by the motor 10. The actuator 13includes a hydraulic cylinder which is operated by pressure oil fedfrom, e.g. the hydraulic pump 12. The actuator 13 is used to drive aworking attachment such as a boom and an arm.

The electric circuit section 100 is configured in such a manner that acircuit 3 for converting power of the generator 2 (a generator powerconverting circuit 3) has an input connected with an output terminal ofthe AC generator 2 and an output connected with a direct-current (DC)line 8 consisting of a power line 8 a and a ground line 8 b.

The generator power converting circuit 3 includes a rectifying circuit18, a smoothing capacitor 19, and a chopper circuit 20. After beingrectified by the rectifying circuit 18, smoothed by the smoothingcapacitor 19, and DC-DC converted by the chopper circuit 20, AC voltagefrom the AC generator 2 is outputted to the DC line 8.

Output terminals 30, 31 of the chopper circuit 20 are respectivelyconnected with the power line 8 a and the ground line 8 b, and inputterminals 44, 45 thereof are respectively connected with the oppositeelectrodes of the smoothing capacitor 19. The configuration of thechopper circuit 20 will be described later.

The generator power converting circuit 3 includes a voltage detectingcircuit 15 for detecting a DC voltage which has been smoothed by thesmoothing capacitor 19. The result of detection by the voltage detectingcircuit 15 is outputted to a power control circuit 23 for calculation.

The chopper circuit 5 has output terminals 30, 31 respectively connectedwith the power line 8 a and the ground line 8 b, and input terminals 44and 45 respectively connected with the positive electrode and thenegative electrode of a battery 4. The configuration of the choppercircuit 5 is substantially identical to that of the chopper circuit 20.The chopper circuit 5 is DC-DC converted between the battery 4 and theDC line 8 to charge and discharge the battery 4.

A voltage detecting circuit 16 is connected between the oppositeelectrodes of the battery 4 to detect a battery voltage Vb. The resultof detection by the voltage detecting circuit 16 is outputted to thepower control circuit 23 for calculation.

The chopper circuit 7 has output terminals 30, 31 respectively connectedwith the power line 8 a and the ground line 8 b, and input terminals 44and 45 respectively connected with the opposite electrodes of acapacitor 6. The configuration of the chopper circuit 7 is substantiallyidentical to that of the chopper circuit 20. The chopper circuit 7 isDC-DC converted between the capacitor 6 and the DC line 8 to charge anddischarge the capacitor 6.

A voltage detecting circuit 17 is connected between the oppositeelectrodes of the capacitor 6 to detected a capacitor voltage Vc. Theresult of detection by the voltage detecting circuit 17 is outputted tothe power control circuit 23 for calculation.

A motor driving circuit 9 has inputs respectively connected with thepower line 8 a and the ground line 8 b of the DC line 8, and outputsconnected with the motor 10. The motor driving circuit 9 drives themotor 10 based on power supplied from at least one of the AC generator2, the battery 4, and the capacitor 6 via the DC line 8. The motordriving circuit 9 has such a circuit configuration as to conform withthe type of the motor 10 such as an induction motor, a DC motor, and asynchronous motor.

A voltage detecting circuit 14 is connected between the power line 8 aand the ground line 8 b to detect a DC voltage. The result of detectionby the voltage detecting circuit 14 is outputted to the power controlcircuit 23 for calculation. A smoothing capacitor 21 is connectedbetween the power line 8 a and the ground line 8 to smooth a higherharmonic wave component included in a DC output voltage from the choppercircuits 5, 7, 20.

A DC voltage command setter 22 sets a DC voltage which is to begenerated between the power line 8 a and the ground line 8 b as a DCvoltage command value Vdc*, and sends the value Vdc* to the powercontrol circuit 23. The DC voltage command value Vdc* is preset based onrating of the motor 10, a withstand voltage of an element constitutingthe motor driving circuit 9, or the like.

In the case where the voltage Vb of the battery 4 and the voltage Vc ofthe capacitor 6 are higher than a voltage Vdc of the DC line 8, diodes36 to 39 in the chopper circuit, which will be described later in FIG.2, are electrically communicable with each other, which makes itimpossible to control the output current by the chopper circuits 20, 5,7. In view of this, the voltage Vdc of the DC line 8 is required to beset higher than the maximal voltage of the battery 4 and the maximalvoltage of the capacitor 6.

Now, the configuration of the chopper circuit 20 (5 or 7) is describedwith reference to FIG. 2. The chopper circuits 20, 5, 7 are eachprovided with semiconductor switching elements 32 to 35, the diodes 36to 39 which are respectively back-to-back connected with thesemiconductor switching elements 32 to 35, a reactor 40, a currentdetecting circuit 41, a current controlling circuit 42, and a pulsewidth modulation (PWM) circuit 43.

The semiconductor switching elements 32 to 35 are each turned on and offin response to a control signal inputted to a control end (not shown)thereof. Examples of the semiconductor switching elements 32 to 35 aresemiconductor elements to be used under large power conditions such asIGBTs and MOS-FETs. The reactor 40 is adapted to smooth an electriccurrent. The current detecting circuit 41 is comprised of a hall elementor a low resistance element, and is adapted to detect a current flowingin the reactor 40, namely, an input current of the chopper circuit 20.The result of detection by the current detecting circuit 41 is outputtedto the current controlling circuit 42.

The current controlling circuit 42 compares the detected current valueoutputted from the current detecting circuit 41 with a current commandvalue outputted from the power control circuit 23, and sends a DCvoltage command value that causes the detected current value to followthe current command value, to the PWM circuit 43.

The PWM circuit 43 outputs to each of the semiconductor switchingelements 32 to 35 an on/off control signal that makes a DC voltagebetween a connecting point 46 of the semiconductor switching elements32, 33, and a connecting point 47 between the semiconductor switchingelements 34, 35 (namely, an input voltage in the chopper circuit 20 or 5or 7) coincident with the DC voltage command value outputted from thecurrent controlling circuit 42.

With the above configuration, the current flowing in the reactor 40 isso regulated as to coincide with the current command value outputtedfrom the power control circuit 23.

As shown in FIG. 1, the current flowing in the reactor 40 of the choppercircuit 20 is a generator current Ig which flows between the choppercircuit 20 and the smoothing capacitor 19, the current flowing in thereactor 40 of the chopper circuit 5 is a battery current Ib which flowsbetween the chopper circuit 5 and the battery 4, and the current flowingin the reactor 40 of the chopper circuit 7 is a capacitor current Icwhich flows between the chopper circuit 7 and the capacitor 6.

Assuming that the currents Ib, Ic flow in the directions shown by thearrows in FIG. 1, the currents Ib, Ic become discharging currents,respectively when Ib>0, Ic>0, whereas the currents Ib, Ic becomecharging currents, respectively when Ib<0, Ic<0.

The chopper circuit 20 (or 5 or 7) shown in FIG. 2 is a well-knownfull-bridge chopper circuit, and is so configured as to allow thereactor 40 to flow the current either in positive or negative directiondesirably by controlling on/off operations of the semiconductorswitching elements 32 to 35.

Referring back to FIG. 1, the power control circuit 23 includes an A/Dconverting circuit 24, a D/A converting circuit 25, a memory 26comprised of an RAM and an ROM, and a CPU 27. The CPU 27 controlsoperations of the respective elements of the power control apparatus inaccordance with a control program stored in the memory 26. The CPU 27has the following functions I), II):

I) function of receiving the DC voltage command value Vdc* which hasbeen set by the DC voltage command setter 22, and receiving, by way ofthe A/D converting circuit 24, the DC voltages Vdc of the DC line 8which have been detected by the voltage detecting circuits 14 through17, a voltage Vg detected at the opposite ends of the smoothingcapacitor 19, the battery voltage Vb of the battery 4, and the capacitorvoltage Vc of the capacitor 6 to calculate a generator current commandvalue Ig*, a battery current command value Ib*, and a capacitor currentcommand value Ic*; and

II) sending the calculated generator current command value Ig*, batterycurrent command value Ib*, and capacitor current command value Ic* tothe chopper circuits 20, 5, 7, respectively by way of the D/A convertingcircuit 25. Control procedures of the respective functions I), II) willbe described later.

In the above configuration, the generator power converting circuit 3(chopper circuit 20) constitutes first power converter, the battery 4and the capacitor 6 respectively constitute storage device, and thechopper circuits 5, 7 respectively constitute second power converter. Inthis embodiment, the capacitor 6 is, for instance, an electric doublelayer capacitor.

FIGS. 3 and 4 are flowcharts showing a control procedure of the CPU 27of the power control circuit 23 in the first embodiment.

First, the DC voltage command value Vdc* is received (in Step 1,hereinafter, Step is called as “ST” such as “ST1”), and then the DCvoltage Vdc of the DC line 8, the voltage Vg detected at the oppositeends of the smoothing capacitor 19, the battery voltage Vb of thebattery 4, and the capacitor voltage Vc of the capacitor 6 are received(in ST2) to be respectively stored in the memory 26.

Next, the following computation is carried out in ST3 by use of thereceived DC voltage command value Vdc* and the DC voltage Vdc of the DCline 8 to obtain a power command value Pw*:ΔVdc=Vdc*−Vdc  (1)Pw _(—) p=Kp·ΔVdc  (2)Pw _(—) I=Pw _(—) I+Ki·ΔVdc  (3)Pw*=Pw _(—) p+Pw _(—) I  (4)

It should be appreciated that the above equations (1) through (4) areknown mathematical expressions for implementing digital PI (proportionalintegration), and Kp, Ki are each a proportionality constant.

Next, in ST4, a generator current command value Ig* to be outputted tothe chopper circuit 20 of the generator power converting circuit 3 iscalculated by implementing the equation (5):Ig*=Pw*/Vg  (5)

Here, the generator power Pw which is supplied from the AC generator 2to the DC line 8 by way of the chopper circuit 20 is equal to theproduct of the generator current Ig which flows between the choppercircuit 20 and the smoothing capacitor 19, and the voltage Vg detectedat the opposite ends of the smoothing capacitor 19.

Namely,Pw=Ig·Vg  (6)

It should be noted that although there exists, in a strict sense, powerwhich is consumed in terms of heat in the chopper circuit 20, such powerconsumption is negligible because the consumed power is insignificantlysmall.

Conversely, if the power command value Pw* is obtained by implementingthe equation (6), the generator current command value Ig* is calculatedby implementing the equation (5).

Next, in ST5, it is judged whether the polarity of the generator poweris positive or negative. As shown in FIG. 1, in this embodiment, thediode rectifying circuit 18 and the smoothing capacitor 19 are used toconvert an AC output voltage of the AC generator 2 to a DC voltage. Ifpower is supplied from the DC line 8 to the smoothing capacitor 19 byway of the chopper circuit 20, there may occur a drawback that thevoltage of the smoothing capacitor 19 is undesirably raised. In view ofthis drawback, it is required to set the generator power at 0 when thepolarity of the generator power is negative based on an assumption thatthe polarity of the generator power is positive in feeding the powerfrom the smoothing capacitor 19 to the DC line 8, and the polaritythereof is negative in feeding the power from the DC line 8 to thesmoothing capacitor 19.

In view of the above, in ST5 of FIG. 3, the polarity of the generatorpower is judged by judging whether Ig*>0. Specifically, if Ig*≦0 (NO inST5), the generator power is set at 0 by setting Ig*=0 (n ST10), and theroutine proceeds to ST11. In ST5, the generator current command valueIg* is used to judge the polarity of the generator power in place of thepower command value Pw*. Since the polarity of the generator power isnot changed because the voltage Vg detected at the opposite ends of thesmoothing capacitor 19 is a DC voltage, this arrangement can obviate thedrawback that the voltage of the smoothing capacitor 19 may beundesirably raised.

On the other hand, if Ig*>0 in ST5 (YES in ST5), it is judged whetherthe calculated generator current command value Ig* exceeds apredetermined limit Igmax (in ST6). If it is judged that Ig* exceeds thelimit Igmax (Ig*>Igmax) (YES in ST6), the limit Igmax is set as thegenerator current command value Ig*(Ig*=Igmax) (in ST7).

Thus, the maximal value of the generator power Pw is controllablyregulated by setting the upper limit of the generator current commandvalue Ig* at a value not larger than the limit Igmax. With thisarrangement, since there is no likelihood that the power to be suppliedfrom the AC generator 2 to the DC line 8 becomes excessively large, thisarrangement can obviate drawbacks such as lowering of the fuelefficiency due to increase of a load of the engine 1, and forciblesuspension of driving of the engine 1 due to overload of the engine 1.

Subsequently, in ST8, by implementing the equation (7), the powercommand value Pw* is redefined by subtracting the maximal value of thegenerator power, i.e. Igmax·Vg (=Ig*·Vg) from the power command valuePw*, and the routine goes to ST11:Pw*=Pw*−Ig*·Vg  (7)

The redefined power command value Pw* represents power in shortagecorresponding to a difference between the maximal value of the generatorpower and demanded power from the load. As will be described later,power corresponding to the redefined power command value Pw* is suppliedeither from the battery 4 or from the capacitor 6, or both from thebattery 4 and the capacitor 6.

On the other hand, if the current command value Ig* does not exceed thelimit Igmax (Ig*≦Igmax) in ST6 (NO in ST6), the generator power issufficiently large to provide demanded power from the load. Accordingly,the command value Ib* of the battery current which flows between thebattery 4 and the chopper circuit 5, and the command value Ic* of thecapacitor current which flows between the capacitor 6 and the choppercircuit 7 are respectively set at 0 (in ST9), and the routine goes toST19.

Next, in ST11, the battery current command value Ib* is calculated byimplementing the equation (8) in a similar manner as in ST4:Ib*=Pw*/Vb  (8)

Next, in ST12, it is judged whether the amplitude (absolute value) ofthe battery current command value Ib* exceeds a predetermined limitIbmax. If it is judged that the amplitude exceeds the limit Ibmax(|Ib*|>Ibmax) (YES in ST12), the following equation (9) is implementedto set the limit Ibmax as the battery current command value Ib* (inST13):Ib*=sgn(Ib*)·Ibmax  (9)

In the equation (9), sgn(Ib*) denotes a signal indicative of thepolarity of the battery current command value Ib*. If Ib*≧0, sgn(Ib*) is+1, whereas if Ib*<0, sgn(Ib*) is −1.

Thus, the battery current Ib, namely, the maximal value ofcharging/discharging currents of the battery 4 is controllably regulatedby setting the upper limit of the amplitude of the battery currentcommand value Ib* at a value not larger than the limit Ibmax. Thisarrangement can obviate drawbacks such as shortening of the useful lifeof the battery 4 and lowering of charging/discharging efficiency of thebattery 4.

Next, in ST14, the power command value Pw* is redefined by subtractingthe maximal value of the battery power, namely, Ib*·Vb, from the powercommand value Pw* by implementing the equation (10), and the routinegoes to ST16:Pw*=Pw*−Ib*·Vb  (10)

The redefined power command value Pw* represents power in shortagecorresponding to a difference between the sum of the maximal value ofthe generator power and the maximal value of the battery power, anddemanded power from the load. As will be described later, in thisembodiment, power corresponding to the redefined power command value Pw*is supplied from the capacitor 6.

On the other hand, in ST12, if the current command value Ib* does notexceed the limit Ibmax in ST12 (Ib*≦Ibmax) (NO in ST12), the sum of thegenerator power and the battery power is sufficiently large to providethe demanded power from the load. Accordingly, the command value Ic* ofthe capacitor current which flows between the capacitor 6 and thechopper circuit 7 is set at 0 (in ST15), and the routine proceeds toST19.

Next, in ST16, the capacitor current command value Ic* is calculated byimplementing the equation (11) in a similar manner as in ST4:Ic*=Pw*/Vc  (11)

Next, in ST17, it is judged whether the amplitude (absolute value) ofthe capacitor current command value Ic* exceeds a predetermined limitIcmax. If it is judged that the amplitude exceeds the limit Icmax(|Ic*|>Icmax) (YES in ST17), the limit Icmax is set as the capacitorcurrent command value Ic* by implementing the equation (12) (in ST18):Ic*=sng(Ic*)·Icmax (12)

It should be noted that, in the equation (12), sgn(Ic*) denotes a signalindicative of the polarity of the battery current command value Ic*. IfIc*≧0, sgn(Ic*) is +1, whereas if Ic*<0, sgn(Ic*) is −1.

In this way, the capacitor current Ic, namely, the maximal value ofcharging/discharging currents of the capacitor 6 is controllablyregulated by setting the upper limit of the amplitude of the capacitorcurrent command value Ic* at a value not larger than the limit Icmax.This arrangement can obviate drawbacks such as shortening of the usefullife of the capacitor 6 and lowering of charging/discharging efficiencyof the capacitor 6.

Next, in ST19, the generator power command value Ig*, the batterycurrent command value Ib*, and the capacitor current command value Ic*,all of which have been obtained according to the aforementioned steps,are sent to the chopper circuits 20, 5, 7, respectively by way of thepower control circuit 23.

In the CPU 27 of the power control circuit 23, the control procedureshown in FIGS. 3 and 4 are cyclically repeated at a predetermined cycle(ranging from several microseconds to several ten microseconds, e.g. 15microseconds.).

Now, the entire operation of the first embodiment is described referringto FIGS. 1 through 4.

First, when the consumption power of the load 11 is varied in responseto an operation of the load 11, power to be supplied and receivedbetween the DC line 8 and the load 11 by way of the motor 10 and thechopper circuit 20 is varied. As a result, power to be supplied to theload 11 from the DC line 8, and power to be supplied to the DC line 8from the AC generator 2, the battery 4, and the capacitor 6 respectivelyby way of the chopper circuits 20, 5, 7 are differentiated from eachother. Thereby, the smoothing capacitor 21 is charged and discharged,with the result that the voltage Vdc of the DC line 8 is varied.

In view of the above, the CPU 27 of the power control circuit 23calculates the power command value Pw* that enables to offset such avoltage variation in steps ST1 through ST3 in FIG. 3. For instance, as aresult of variation of the voltage Vdc of the DC line 8, the powercommand value Pw* is increased.

Subsequently, it is judged, in steps ST4 through ST10, whether powercorresponding to the power command value Pw* is sufficiently suppliablesolely from the AC generator 2. If it is judged that such power issuppliable from the AC generator 2, a generator current command valueIg* corresponding to the power command value Pw* is calculated, and thecalculated generator current command value Ig* is sent from the powercontrol circuit 23 to the chopper circuit 20, which in turn controls thegenerator current Ig to coincide with the generator current commandvalue Ig*. As a result of the control, power to be outputted from thechopper circuit 20 is increased, whereby the voltage Vdc of the DC line8 is controllably rendered coincident with the DC voltage command valueVdc*. In the case where the polarity of the power command value Pw* isnegative, as described above, the generator current command value Ig* isset at 0.

On other hand, in the case where power from the AC generator 2 is notsufficiently large to provide power corresponding to the power commandvalue Pw*, in steps ST11 through ST15, it is judged whether powercorresponding to a difference between the power command value Pw* andthe generator power (=Ig·Vg) is suppliable solely from the battery 4. Ifit is judged that the power is suppliable from the battery 4, a batterycurrent command value Ib* corresponding to the aforementioned differenceis calculated, and the calculated battery current command Ib* is sentfrom the power control circuit 23 to the chopper circuit 5, which inturn controls the battery current Ib to coincide with the calculatedbattery current command value Ib*. As a result of the control, the sumof output voltages from the chopper circuits 20 and 5 is increased,whereby the voltage Vdc of the DC line 8 is controllably renderedcoincident with the voltage command value Vdc*.

Further, in the case where the sum of the powers from the AC generator 2and the battery 4 is not sufficiently large to provide powercorresponding to the power command value Pw*, in steps ST16 through ST19in a similar manner as mentioned above, a capacitor current commandvalue Ic* is calculated in such a manner as to allow the capacitor 6 tosupply power in shortage, the calculated command value Ic* is sent fromthe power control circuit 23 to the chopper circuit 7, which in turncontrols the capacitor current Ic to coincide with the capacitor currentcommand value Ic*. As a result of the control, the sum of outputvoltages from the chopper circuits 20, 5, 7 is increased, whereby thevoltage Vdc of the DC line 8 is controllably rendered coincident withthe voltage command value Vdc*.

By implementing the above operations, even if power demanded from theload 11 is varied, the voltage Vdc of the DC line 8 is securelymaintained at a constant level.

Thus, according to the first embodiment, the chopper circuits 20, 5, 7are provided respectively between the DC line 8, and the AC generator 2,the battery 4, and the capacitor 6, calculated is the power commandvalue Pw* required for retaining the voltage Vdc of the DC line 8 at thevoltage command value Vdc*, and calculated are the generator currentcommand value Ig*, the battery current command value Ib*, and thecapacitor current command value Ic* required for satisfying the powercommand value Pw* to thereby controllably flow currents corresponding tothe current command values Ig*, Ib*, Ic* in the chopper circuits 20, 5,7, respectively. With this arrangement, even if the power demand fromthe load 11 is greatly varied, the voltage Vdc of the DC line 8 can bemaintained at a substantially constant value, namely, at a valueapproximate to the voltage command value Vdc*.

The above arrangement eliminates necessity of adopting elements havinghigh durability as circuit elements including the semiconductorswitching elements 32 through 35 used in the chopper circuits 20, 5, 7,and a circuit element used in the motor-driving circuit 9. Accordingly,the chopper circuits 20, 5, 7, and the motor-driving circuit 9 can beconfigured at a low cost.

Further, according to the first embodiment, the maximal value of thegenerator current Ig which is outputted from the AC generator 2 is setat a value not larger than the predetermined limit Igmax. Even if thepower demand from the load 11 is abruptly increased, this arrangementcan obviate drawbacks such as lowering of the fuel efficiency of theengine 1 and forcible suspension of driving of the engine 1.

Further, according to the first embodiment, the maximal value of thebattery current Ib and the maximal value of the amplitude of thecapacitor current Ic are respectively set at values not larger than thelimits Ibmax and Icmax. Even if the power demand from the load 11 isabruptly increased, this arrangement can obviate drawbacks such asshortening of the useful life of the battery 4 and the capacitor 6, andlowering of charging/discharging efficiency thereof.

Further, there is proposed a construction machine in which outputterminals of a plurality of storage device having input/outputcharacteristics different from each other are directly connected with aDC line to selectively change over the plurality of storage device to beused depending on a varying load characteristic (see Japanese UnexaminedPatent Publication No. 2000-295717). Directly connecting the pluralityof storage device with the DC line may likely to cause supplying andreceiving of power between or among the plurality of storage device. Asa result, power distribution is determined by the relation between theterminal voltage of each storage device and the output impedance.

On the contrary, according to the first embodiment of the invention,since the chopper circuit 5 (7) is provided between the battery 4(capacitor 6) and the DC line 8, there is no likelihood that power issupplied and received between the battery 4 (capacitor 6) and the DCline 8. Thus, this arrangement can obviate a drawback that controlefficiency of the power control apparatus is lowered as a whole due topower loss resulting from such power supplying and receiving. Further,power distribution is desirably controlled in such a manner that thebattery 4 and the capacitor 6 can attain their respective optimalefficiencies depending on the input/output characteristics thereof.

(b) Second Embodiment

Now, a power control apparatus for use in a hybrid vehicle in accordancewith a second embodiment of the invention is described. The electricalconfiguration of the second embodiment is identical to that of the firstembodiment shown in FIGS. 1 and 2 except that the second embodiment isdifferent from the first embodiment in control procedure of the CPU 27(see FIG. 1) of the power control circuit 23.

FIGS. 5 and 6 are flowcharts of the control procedure of a CPU 27 of apower control circuit 23 in the second embodiment.

Referring to FIG. 5, steps ST30 through ST32 are identical to steps ST1through ST3 in FIG. 3, and accordingly, description thereof is omittedherein.

In ST33, a capacitor current command value Ic*, which is a command valueof a capacitor current Ic flowing in a chopper circuit 7, is calculatedby using a capacitor voltage Vc received in ST31 and a power commandvalue Pw* calculated in ST32 by implementing the equation (13):Ic*=Pw*/Vc  (13)

Subsequently, in ST34, it is judged whether the polarity of thecapacitor current command value Ic* is positive or negative, namely,IC*>0. Here in the second embodiment, the polarity of the capacitorcurrent command value Ic* is positive when a capacitor 6 is discharged,whereas the polarity thereof is negative when the capacitor 6 ischarged.

If it is judged that the polarity of the capacitor current command valueIc* is positive, namely, the capacitor 6 is discharged (YES in ST34),then, it is judged whether the capacitor voltage Vc is not larger than apredetermined minimal value Vcmin. If it is judged that Vc≦Vcmin (YES inST35), the capacitor current command value Ic*=0 (in ST36), and theroutine proceeds to ST47. At this time, the capacitor 6 is notdischarged because the judgment result shows that the capacitor voltageVc of the capacitor 6 is too low. Therefore, demanded power is suppliedeither from a battery 4 or from an AC generator 2 or both from thebattery 4 and the AC generator 2, which will be described later.

On the other hand, if it is judged that Vc>Vcmin (NO in ST35), it isjudged whether the capacitor current command value Ic* is not smallerthan a predetermined maximal value Icmax (in ST37). If it is judged thatIc*≧Icmax (YES in ST37), the maximal value Icmax is set as the capacitorcurrent command value Ic* (in ST38), and a value which is obtained bysubtracting the maximal value of the capacitor power, namely, Icmax·Vc,from the power command value Pw* is redefined as the power command valuePw* by implementing the equation (14) (in ST39):Pw*=Pw*−Ic*·Vc  (14)Power corresponding to the power command value Pw* is supplied eitherfrom the battery 4 or from the AC generator 2 or both from the battery 4and the AC generator 2, which will be described later.

On the other hand, if it is judged that Ic*<Icmax (NO in ST37), agenerator current command value Ig* and a battery current command valueIb* are respectively set at 0 (in ST40) because power supplied bydischarging of the capacitor 6 is sufficiently large to provide demandedpower from the load. Then, this routine goes to ST57.

In ST34 where it is judged whether the polarity of the capacitor currentcommand value Ic* is positive or negative, judgment that the polarity isnegative, namely, the capacitor 6 is charged means that there existssurplus power. In such a case (NO in ST34), it is judged in ST41 whetherthe capacitor voltage Vc exceeds the predetermined maximal value Vcmax.If it is judged that Vc≧Vcmax (YES in ST41), the capacitor currentcommand value Ic*=0 (n ST42), and the routine proceeds to ST47. At thistime, the capacitor 6 is not charged because the judgment result showsthat the capacitor voltage Vc of the capacitor 6 is too high. Surpluspower is used for charging the battery 4, which will be described later.

On the other hand, if it is judged that Vc<Vcmax (NO in ST41), then, itis judged whether the capacitor current command value Ic* is not largerthan the predetermined minimal value Icmin (in ST43). If it is judgedthat Ic*≦Icmin (YES in ST43), the minimal value Icmin is set as thecapacitor current command value Ic* (in ST44), and a value which isobtained by subtracting the minimal value of the capacitor power,namely, Icmin·Vc, from the power command value Pw* is redefined as thepower command value Pw* by implementing the equation (15) (in ST45):Pw*=Pw*−Ic*·Vc  (15)Surplus power is used for charging the battery 4, which will bedescribed later.

On the other hand, if it is judged that Ic*>Icmin (NO in ST43), thegenerator current command value Ig* and the battery current commandvalue Ib* are respectively set at 0 (in ST46) because the capacitor 6 issufficiently charged, and there is no need of using the surplus power.Then, the routine goes to ST57.

As mentioned above, the capacitor current command value Ic* iscalculated by implementing steps ST33 through ST46.

Judgment in ST34 that the polarity of the capacitor current commandvalue Ic* is positive, namely, the capacitor 6 is discharged means thatthe discharged power is supplied to the load 11 by way of the DC line 8.There may be a case that power discharged from the capacitor 6 is notsufficiently large to provide demanded power from the load 11. In such acase, power in shortage is supplied either from the battery 4 or fromthe AC generator 2, or both from the battery 4 and the AC generator 2.

On the other hand, judgment in ST34 that the polarity of the capacitorcurrent command value Ic* is negative, namely, the capacitor 6 ischarged means that surplus power is supplied from the DC line 8 to thecapacitor 6 since the load 11 is a light load. In such a case, since thebattery 4 and the capacitor 6 serve as means for charging, the surpluspower is handled (namely, the battery 4 is charged) in the case wherethere still remains surplus power after charging the capacitor 6.

Steps ST47 through ST50 are identical to steps ST11 through ST14 in FIG.3. In ST50, a value which is obtained by subtracting a maximal value ofthe battery power, namely, Ibmax·Vb, from the power command value Pw* isredefined as the power command value Pw* by implementing the equation(16):Pw*=PW*−Ib*·Vb  (16)Power corresponding to the power command value Pw* is supplied from theAC generator 2, which will be described later.

On the other hand, in ST48, if it is judged that the amplitude (absolutevalue) of the battery current command value Ib* does not exceed apredetermined maximal value Ibmax (NO in ST48), the generator currentcommand value Ig* is set at 0 (in ST51) because power supply from the ACgenerator 2 is not necessary. Then, this routine goes to ST57.

Next, in ST52, the generator current command value Ig* which isoutputted to a chopper circuit 20 of a generator power convertingcircuit 3 is calculated by implementing the equation (17):Ig*=Pw*/Vg  (17)Next, in ST53, it is judged whether the polarity of the generatorcurrent command value Ig* is positive or negative.

If it is judged that Ig*≦0 (NO in ST53), the generator power is set at 0by setting Ig*=0 (in ST56). Then, the routine goes to ST57. Thisarrangement can obviate a phenomenon that the voltage of a smoothingcapacitor 19 is abruptly raised because there is no likelihood thatpower may be supplied from the DC line 8 to the smoothing capacitor 19by way of the chopper circuit 20.

On the other hand, if it is judged that Ig*>0 in ST53 (YES in ST53), itis judged whether the calculated generator current command value Ig*exceeds a predetermined limit Igmax (in ST54). If it is judged that thevalue Ig* exceeds the limit Igmax (Ig*>Igmax) (YES in ST54), the limitIgmax is set as the generator current command value Ig* (Ig*=Igmax) (inST55). Then, this routine goes to ST57.

In this way, as with the case of the first embodiment, the maximal valueof the generator power Pw is controllably regulated by setting the upperlimit of the generator current command value Ig* at a value not largerthan the limit Igmax. This arrangement can obviate drawbacks such aslowering of the fuel efficiency due to increase of a load of the engine1 or forcible suspension of driving of the engine 1 due to overload ofthe engine 1, because there is no likelihood that power to be suppliedfrom the AC generator 2 to the DC line 8 is excessively large.

Next, in ST57, the generator current command value Ig*, the batterycurrent command value Ib* and the capacitor current command value Ic*which have been obtained by implementing the aforementioned steps arerespectively sent to the chopper circuits 20, 5, 7 by way of the powercontrol circuit 23.

The generator current Ig, the battery current Ib, and the capacitorcurrent Ic are so controlled as to cause these currents Ig, Ib, Ic tofollow the current command values Ig*, Ib*, Ic*, respectively by thechopper circuit 20, 5, 7. As a result of the control, even ifconsumption power of the load 11 is varied depending on an operation ofthe load 11, the voltage Vdc of the DC line 8 is securely maintained ata constant level.

According to the second embodiment, as with the case of the firstembodiment, calculated are the generator current command value Ig*, thebattery current command value Ib*, and the capacitor current commandvalue Ic* required for satisfying the power command value Pw* so as tocontrollably allow currents corresponding to the current command valuesIg*, Ib*, Ic* to flow. With this arrangement, even if power demand fordriving the load 11 is greatly varied, the voltage Vdc of the DC line 8can be maintained at a substantially constant value, namely, at a valueapproximate to the voltage command value Vdc*. Thus, a similar effect asthe first embodiment is obtainable in the second embodiment.

Further, according to the second embodiment, the current command valuesare calculated in the order of the capacitor current command value Ic*,the battery current command value Ib*, and the generator current commandvalue Ig*, which is different from the order in the first embodiment.Namely, charging/discharging of the capacitor 6 comes first in thesecond embodiment. With this arrangement, even if power demand from theload 11 to the DC line 8 is abruptly increased, such power demand isproperly satisfied by charging operation of the capacitor 6 having ahigher charging ability per unit time than the battery 4. Accordingly,variation of the voltage Vdc of the DC line 8 can be more effectivelysuppressed. Thus, in the second embodiment, power distribution iscontrolled in such a manner that the battery 4 and the capacitor 6 canattain their respective optimal efficiencies depending on input/outputcharacteristics of the battery 4 and the capacitor 6. It should be notedthat when the load 11 receives power supply from the DC line 8,discharging of the capacitor 6 is carried out prior to receiving of thepower by the load 11, thereby having sufficient charging ability to copewith a case that charging operation is required as a result of sharprise of power demand from the load 11 to the DC line 8.

Further, according to the second embodiment, since the voltage Vc of thecapacitor 6 is so regulated as to fall in a range having thepredetermined minimal value Vcmin and the predetermined maximal valueVcmax, the useful life of the capacitor 6 can be further extended,compared with the first embodiment.

In the foregoing embodiments, described is the arrangement equipped witha single set of the load 11, the motor 10, and the generator-drivingcircuit 9. This invention is not limited to the foregoing embodiments. Asimilar effect as in the foregoing embodiments is obtained in anarrangement equipped with two or more sets of the above components.

Further, in the above embodiments, described is the arrangement wherethe battery 4 and the capacitor 6 constitute the storage device. Thisinvention is not limited to the above embodiments. Alternatively, thestorage device may have at least one of a battery and a capacitor. Forinstance, alternatively proposed are an arrangement provided with aplurality of batteries including a battery 4, an arrangement providedwith a plurality of capacitors including a capacitor 6, an arrangementprovided with a plurality of batteries and a plurality of capacitors, anarrangement merely provided with a battery 4, and an arrangement merelyprovided with a capacitor 6.

Further, in the above embodiments, the actuator 13 may be a hydraulicmotor for a running body or a swing body to drive, e.g., a crawler.Further, in the above embodiments, the load 11 may be a reducer in caseof directly driving a crawler by a motor or a case of driving wheels ofa generally available hybrid vehicle.

(c) Third Embodiment

Next, an embodiment of a hybrid construction machine according to thisinvention is described as a third embodiment of the invention. FIG. 7 isa diagram showing an entire construction of a hybrid hydraulic excavatoras the third embodiment. It should be noted that elements of the thirdembodiment identical to those of the first embodiment are denoted at thesame reference numerals.

The hydraulic excavator is comprised of, as shown in FIG. 7, a lowertraveling body 101, an upper rotating body 102, and an excavationattachment 103 which is mounted on a front part of the upper rotatingbody 102. The hydraulic excavator further comprises a power controlapparatus in accordance with the first embodiment of the invention.

The lower traveling body 101 includes a right-side crawler frame 104 anda left-side crawler frame 105 provided laterally at the opposite sidesthereof (in FIG. 7, only one of the crawler frames is illustrated). Thecrawler frames 105 (sic) are individually rotated by motors (not shown)for driving the running body.

The upper rotating body 102 is comprised of a rotating frame 106 and acabin 107. On the rotating frame 106, mounted are an engine 1 as a powersource, an AC generator 2 driven by the engine 1, a battery 4, a motor10D for driving the upper rotating body 102, a reducer 11A which reducesrotating force of the swing-driving motor 10D to transmit the rotatingforce to a swing mechanism (swing gear), a motor 10A for driving a boom,a hydraulic pump 12A which is rotated by the boom-driving motor 10A, andan electrical circuit section 100.

The excavation attachment 103 is comprised of a boom 108, a boomcylinder 13A which is operatively expanded and contracted in response tohydraulic oil supplied from the boom-driving hydraulic pump 12A to movethe boom up and down, an arm 109, an arm cylinder 13B for pivoting thearm 109, a bucket 110, and a bucket cylinder 13C for operating thebucket 110.

An arm-driving motor 10B and an arm-driving hydraulic pump 12B which isdriven by the motor 10B are mounted on the arm cylinder 13B of theexcavation attachment 103. A bucket-driving motor 10C and abucket-driving hydraulic pump 12C which is driven by the motor 10C aremounted on the bucket cylinder 13C.

To summarize this embodiment, the hydraulic excavator in accordance withthis embodiment is comprised of the electric circuit section 100corresponding to the electric circuit section 100 of the firstembodiment; the boom-driving motor 10A, the arm-driving motor 10B, thebucket-driving motor 10C, the swing-driving motor 10D, and the pair ofrunning-driving motors (not shown) which correspond to the motor 10 (seeFIG. 1) of the first embodiment; the reducer 11A corresponding to theload 11 (see FIG. 1); the boom-driving hydraulic pump 12A, thearm-driving hydraulic pump 12B, and the bucket-driving hydraulic pump12C which correspond to the hydraulic pump 12 (FIG. 1); and the boomcylinder 13A, the arm cylinder 13B, and the bucket cylinder 13C whichcorrespond to the actuator 13 (see FIG. 1).

According to this embodiment, the hydraulic excavator having a similareffect as in the first embodiment is attained. Alternatively, thehydraulic excavator in accordance with the third embodiment may beloaded with the power control apparatus in accordance with the secondembodiment, in place of the power control apparatus in accordance withthe first embodiment. Further, in this embodiment, a hybrid hydraulicexcavator is described as an example of the inventive hybridconstruction machine. Alternatively, this invention can be applied toother hybrid construction machines such as a hybrid hydraulic crane.

Exploitation in Industry

As mentioned above, this invention is useful in various hybrid vehiclesloaded with an engine and an electric motor to drive a load by themotor. Particularly, this invention is suitable for use in constructionmachines such as hydraulic excavators and hydraulic cranes in which aload is varied during operation of the machine.

1. A power control apparatus for a hybrid vehicle provided with anengine, a generator driven by the engine, at least one storage device,an electric motor driven by electric power supplied from at least one ofthe generator and the storage device, and a load operated by the motoras a drive source, the power control apparatus comprising: a first powerconverter provided between said generator and a direct-current line forconverting the power outputted from the generator to DC power to outputthe DC power to said direct-current line; at least one second powerconverter provided between said storage device and said direct-currentline for converting the power outputted from said storage device to DCpower to output the DC power to said direct-current line; a motor driverelectrically connected with said direct-current line for driving saidmotor based on the power supplied by way of the direct-current line; anda power controller for controlling said first power converter and saidsecond power converter to output DC power corresponding to demandedpower for said load by way of said motor to said direct-current line,wherein said power controller controls said first power converter andsaid second power converter to maintain a voltage of said direct-currentline at a substantially constant level irrespective of wide variation ofthe demanded power for said load.
 2. A power control apparatus for ahybrid vehicle according to claim 1, wherein said power controllercontrols said first power converter to output the DC power of a valuenot larger than a predetermined value.
 3. A power control apparatus fora hybrid vehicle according to claim 1, wherein said power controllercontrols said storage device to discharge an electric current of a valuenot larger than a predetermined value and to charge an electric currentof a value not larger than a predetermined value.
 4. A power controlapparatus for a hybrid vehicle according to claim 1, wherein said powercontroller controls said second power converter to output the DC powerin such a manner that said storage device outputs a DC voltage of avalue not larger than a predetermined value.
 5. A power controlapparatus for a hybrid vehicle according to claim 1, wherein said powercontroller controls said second power converter to output the DC powerin such a manner that said storage device outputs a DC voltage of avalue not smaller than a predetermined value.
 6. A power controlapparatus for a hybrid vehicle according to claim 1, wherein said powercontroller controls said second power converter to output the DC powerin such a manner that electric energy stored in said storage device liesin a predetermined range.
 7. A power control apparatus for a hybridvehicle according to claim 1, wherein said power controller includes afirst controller for sending an electrical command signal to said firstpower converter, and a second controller for sending an electricalcommand signal to said second power converter; said first powerconverter outputs the DC power responsive to the electrical commandsignal from said first controller; said second power converter outputsthe DC power responsive to the electrical command signal from saidsecond controller; and each of said first controller and said secondcontroller sends the electrical command signal operative to maintain thevoltage of said direct-current line at a substantially constant level.8. A power control apparatus for a hybrid vehicle according to claim 1,further comprising a plurality of said storage device, and a pluralityof said second power converter corresponding to said plurality ofstorage device in number.
 9. A power control apparatus for a hybridvehicle according to claim 8, wherein said power controller controlssaid plurality of second power converter in accordance with apredetermined order or priority based on input/output characteristics ofeach of said plurality of storage device in controlling said pluralityof second power converter in response to the demanded power for saidload.
 10. A power control apparatus for a hybrid vehicle according toclaim 1, wherein said load includes an actuator for actuating a workingattachment mounted on a main body of the hybrid vehicle.
 11. A hybridconstruction machine comprising: an engine; a generator driven by theengine; a storage device; an electric motor driven by electric powersupplied from at least one of the generator and the storage device; aload including an actuator for actuating a working attachment; and apower control apparatus including: a first power converter providedbetween said generator and a direct-current (DC) line for converting thepower output from the generator to DC power to output the DC power tosaid DC line; a second power converter provided between said storagedevice and said DC line for converting the power output from saidstorage device to DC power to output the DC power to said DC line; amotor driver electrically connected with said DC line for driving saidmotor based on the power supplied by way of the DC line; and a powercontroller for controlling said first power converter and said secondpower converter to output DC power corresponding to demanded power forsaid actuator by way of said motor to said DC line, said powercontroller controlling said first power converter and said second powerconverter to maintain a voltage of said DC line at a substantiallyconstant level irrespective of wide variation of the demanded power forsaid load.
 12. A hybrid construction machine according to claim 11,wherein said power controller controls said first power converter tooutput the DC power of a value not larger than a predetermined value.13. A hybrid construction machine according to claim 11, wherein saidpower controller controls said storage device to discharge an electriccurrent of a value not larger than a predetermined value and to chargean electric current of a value not larger than a predetermined value.14. A hybrid construction machine according to claim 11, wherein saidpower controller controls said second power converter to output the DCpower in such a manner that said storage device outputs a DC voltage ofa value not larger than a predetermined value.
 15. A hybrid constructionmachine according to claim 11, wherein said power controller controlssaid second power converter to output the DC power such that saidstorage device outputs a DC voltage of a value not smaller than apredetermined value.
 16. A hybrid construction machine according toclaim 11, wherein said power controller controls said second powerconverter to output the DC power such that electric energy stored insaid storage device lies in a predetermined range.
 17. A hybridconstruction machine according to claim 11, wherein said powercontroller includes a first controller for sending an electrical commandsignal to said first power converter, and a second controller forsending an electrical command signal to said second power converter;said first power converter outputs the DC power responsive to theelectrical command signal from said first controller; said second powerconverter outputs the DC power responsive to the electrical commandsignal from said second controller; and each of said first controllerand said second controller sends the electrical command signal operativeto maintain the voltage of said DC line at a substantially constantlevel.
 18. A hybrid construction machine according to claim 11, furthercomprising a plurality of said storage devices, and a plurality of saidsecond power converters corresponding to said plurality of storagedevices in number.
 19. A hybrid construction machine according to claim18, wherein said power controller controls said plurality of secondpower converters in accordance with a predetermined order or prioritybased on input/output characteristics of each of said plurality ofstorage devices in controlling said plurality of second power convertersin response to demanded power for said actuator.
 20. A power controlapparatus for a hybrid vehicle provided with an engine, a generatordriven by the engine, at least one storage device, an electric motordriven by electric power supplied from at least one of the generator andthe storage device, and a load operated by the motor as a drive source,the power control apparatus comprising: a first power converter providedbetween said generator and a direct-current line for converting thepower outputted from the generator to DC power to output the DC power tosaid direct-current line; at least one second power converter providedbetween said storage device and said direct-current line for convertingthe power outputted from said storage device to DC power to output theDC power to said direct-current line; a motor driver electricallyconnected with said direct-current line for driving said motor based onthe power supplied by way of the direct-current line; and a powercontroller for controlling said first power converter and said secondpower converter to output DC power corresponding to demanded power forsaid load by way of said motor to said direct-current line, wherein saidpower controller controls said first power converter and said secondpower converter to maintain a voltage of said direct-current line at asubstantially constant level irrespective of wide variation or drasticchange of the demanded power for said load.
 21. A hybrid constructionmachine comprising: an engine; a generator driven by the engine; astorage device; an electric motor driven by electric power supplied fromat least one of the generator and the storage device; a load includingan actuator for actuating a working attachment; and a power controlapparatus including: a first power converter provided between saidgenerator and a direct-current (DC) line for converting the power outputfrom the generator to DC power to output the DC power to said DC line; asecond power converter provided between said storage device and said DCline for converting the power output from said storage device to DCpower to output the DC power to said DC line; a motor driverelectrically connected with said DC line for driving said motor based onthe power supplied by way of the DC line; and a power controller forcontrolling said first power converter and said second power converterto output DC power corresponding to demanded power for said actuator byway of said motor to said DC line, said power controller controllingsaid first power converter and said second power converter to maintain avoltage of said DC line at a substantially constant level irrespectiveof wide variation or drastic change of the demanded power for said load.